The present invention relates to a method and an apparatus for three-dimensional exploration wherein location of an object present within a medium is found by transmitting wave signals by means of an electromagnetic wave or sonic wave into the medium in the course of movement over the surface of the medium and receiving the signals reflected from the object within the medium and processing the received reflected-signals. The invention relates also to a method and an apparatus for displaying three-dimensional voxel data generated in the form of coordinates (x, y, t) consisting of a position (x, y) on the surface of the medium and a reflection time (t) based on a reflected signal intensity of a wave signal transmitted from the surface of medium into this medium.
For the three-dimensional exploration as noted above, a three-dimensional exploratory apparatus is employed for exploring an object or a hollow space buried or present underground.
A typical conventional art is known from a paper entitled: xe2x80x9cUnderground Buried Object Exploring Radar System (Part 3); Three-Dimensional Exploration Image Processingxe2x80x9d (National Convention of The Institute of Electrical Engineers of Japan, 63rd year of Showa, p 1372).
According to this art (first prior art), measured section information obtained by a plurality of cycles of scanning operations is used. If an image of the buried unidentified object is obtained at identical positions in all of the plurality of section images, then the buried object is judged as a pipe. Whereas, if the image of the buried object is obtained at identical positions in fewer than all of the section images, the buried object is then judged as a block object. By determining the connectivity/non-connectivity between the images present in different sections, the three-dimensional structure is obtained.
In the above, only one kind of threshold value is employed in a binary encoding scheme based on which the presence/absence of the object is to be judged.
With the above-described prior art, the symbolic representations of the respective sections (e.g. binary symbol representation representing presence/absence of the object according to the reflected signal intensity) are connected three-dimensionally. Hence, the setting of the threshold value employed for the symbolizing scheme significantly influences the determination of the unidentified object either as a pipe or as a block object. Especially, in the case of underground exploration, the S/N ratio is low and the intensity of the reflected signal from the object can vary significantly with change of the exploring position. Therefore, in binarizing the reflected signal according to its intensity, if the threshold value is significantly lowered to enable detection of the pipe, this will lead to occurrence of a large amount of noise region of e.g. unwanted reflected signals. This is because the information about the neighboring sections is not utilized at all for the binarizing process.
Moreover, this prior art requires that the buried pipe be oriented in a direction perpendicular to the scanning direction of the apparatus. Therefore, although the symbolizing method as above may be useful on such prerequisite, the reliability of exploration is reduced when the buried pipe is not oriented in the direction perpendicular to the scanning direction.
Also, with the three-dimensional exploratory apparatus, the electromagnetic wave is transmitted into the ground at a position (x, y) on the ground surface and the signal reflected from the buried object is received, in the course of which the reflected signal intensity (s) is determined at every reflected time (t) of a predetermined interval. Therefore, if positions (x, y) on the ground surface of the three-dimensional exploratory apparatus are taken in the form of a grating pattern of a predetermined spacing, it is possible to obtain complete three-dimensional voxel data s (x, y, t) having data values (reflected signal intensities (s)) at all of its voxels. However, when the three-dimensional exploratory apparatus is scanned on the ground surface, depending on the actual surface condition of the exploration site such as the ground surface being a road surface, it is not always possible to effect this scanning operation exactly in the form of grating pattern, due to safety and/or time restriction. Then, while the data measurement can be done densely in the direction of the reflection time (t), both voxels having data values and voxels not having any data values coexist in the x-y plane. Here, for such three-dimensional voxel data, a voxel having a data value is defined as a source voxel and a voxel not having any data value is defined as a deficient voxel.
Conventionally, as a method of interpolating such a deficient voxel in such three-dimensional voxel data which are irregularly present in the x-y plane, it is well-known, as a second prior art, to effect weighting of the interpolation according to its distance from a source voxel. According to this prior art, when the distance between a deficient voxel and a source voxel (voxel value (s)) is D, the interpolation for this deficient voxel is done with a value (sxe2x80x2) obtained by the following formula 1:
Sxe2x80x2=(xcexa3Dxe2x88x92Es)/(xcexa3Dxe2x88x92E)xe2x80x83xe2x80x83(1)
where, E is provided for adjusting the degree of weighting, which can be a numerical value of 3, 5, etc. This numerical value will be appropriately selected, depending on the density of the data to be interpolated and/or dispersion of the voxel values. This interpolation can be done three-dimensionally. However, since the data are present densely in the direction of the reflection time (t), this interpolation is rather considered as interpolation of two-dimensional data within the x-y plane. Then, by effecting the interpolation at each reflection time (t) interval with using the obtained weighting value for the two-dimensional plane, the amount of calculation needed may be significantly reduced.
If the interpolation of three-dimensional voxel data is effected according to the above-described prior art, whether it is effected three-dimensionally or two-dimensionally, the following three problems occur.
Firstly, when another source voxel is present at a slightly distant location along the same direction from a deficient voxel to be interpolated toward a source voxel and these two source voxels have significantly differing data values (e.g. when their signs are different being positive or negative), the target value for the deficient voxel to be interpolated may be influenced also by the value of the distant source voxel.
Secondly, since the interpolation is effected in accordance with the distance alone, that is, without considering the direction, an extrapolation which generates a value far less reliable than obtained with an interpolation may also take place inadvertently.
Thirdly, if no source voxel at all is present in the vicinity of the deficient voxel, the interpolation will be effected anyway in a forcible manner by using the data value of a very distant source voxel, whereby the precision of the interpolated value will suffer considerably.
As a method devised for solving the first and second problems noted above, there is known a second conventional method. With this method, a Delaunay triangulation diagram is obtained by calculations from the two-dimensional distribution of source voxels in the x-y plane. Then, for a deficient voxel present within each triangle of the diagram, by using a data value of a source voxel present at the apex of this triangle, an interpolation operation is effected for the deficient voxel with a weighting corresponding to its distance therefrom. However, in order to obtain such Delaunay triangulation diagram by calculations, if xe2x80x98nxe2x80x99 units of source voxels are present in the two-dimensional distribution thereof within the x-y plane, a vast amount of calculations on the order of n2 to n3 will be necessary. Moreover, the third problem remains unsolved.
As a third prior art, the following method is also known. In this method, for displaying the three-dimensional voxel data, in the case of an underground buried object exploration for example, a wave signal by means of an electromagnetic wave or sonic wave is transmitted into the ground while movement over the ground surface and the signal reflected from the underground object is received. Then, based on the intensity of this reflected signal, three-dimensional voxel data are generated in the form of coordinates (x, y, t) consisting of the position (x, y) on the ground surface and the reflection time (t). Usually, this method needs an enormous amount of operation requiring much trouble and skill for generating a number of images from such three-dimensional voxel data obtained along a plurality of vertical or horizontal sections and then displaying them for comparison analysis thereof For instance, FIG. 26 shows an example of image display showing three-dimensional voxel data of a buried condition of FIG. 13 along a horizontal section. In the case of this section display, only a section of a fixed depth can be displayed. Then, in order to grasp the condition of an object buried at a different depth, another display will be needed with changing the depth.
In an attempt to overcome the problem of the third conventional art, The Institute of Electronics, Information and Communication Engineers: transactions: category D (Vol. J71-D No. 10, pp2002-2009) entitled: xe2x80x9cThree-Dimensional Data Displaying Method for Under-Snow Radar Systemxe2x80x9d proposes, as a fourth prior art, a method contemplating how to display the entire information of three-dimensional data in the form of a two-dimensional image.
FIGS. 27 through 29 illustrate display examples which were obtained by employing one mode, referred to as a surface display method, of the above-described fourth prior art described above for displaying the three-dimensional voxel data of the buried condition of FIG. 13. FIG. 27, FIG. 28 and FIG. 29 illustrate three examples in which the threshold value was varied from high, medium to low in the mentioned order in order to seek for an appropriate threshold value. From these, it may be understood that with high threshold value, the reflected signal becomes intermittent to impede the discrimination of the buried object, whereas with low threshold reflected signals of smaller intensities too can be displayed, but due to low S/N ratio of the reflected signals per se noise components are displayed also so as to deteriorate the visibility.
Next, FIG. 30 illustrates a display example which was obtained by employing another mode, referred to as an integration method, of the above-described fourth prior art which has been conventionally employed in e.g. ultrasonic diagnosis, for the same three-dimensional voxel data of the buried condition of FIG. 13 in the axis direction of reflection time (t). In this case too, since the S/N ratio of the reflected signals per se is low and also the area of the buried object is rather small relative to the entire exploration area, there occurs reduction in the image contrast due to the effect of integration, thus the visibility is again deteriorated. In addition to these methods, a difference addition method, a product sum method, etc. have also been proposed. However, since these methods employ difference from an adjacent value, there occurs the problem of enhancement of fine noises in the case of data of low S/N ratio.
The present invention has been made in view of the above-described state of the art. Its first object is to detect location of an underground buried object with high S/N ratio through effective interaction between a three-dimensional processing using a value of a neighboring section (voxel) and an manual operation. The second object of the invention is to provide a method or means which affords easy interpolation of a deficient voxel when such voxel deficient in data is present in three-dimensional voxel data so as to enable high-efficiency and high-precision detection of location of the underground buried object. The third object of the invention is to provide a method and an apparatus for displaying three-dimensional voxel data with low SIN ratio by means of a simple two-dimensional image display so as to allow easier and more accurate grasp of an object or the like present within a medium.
For accomplishing the first object note above, a three-dimensional exploring method relating to the present invention is characterized by the first through seventh characterizing features as follows.
According to the first charactelizing feature, in a three-dimensional exploring method for finding location of an object present within a medium by sequentially effecting an transmitting/receiving step of transmitting a wave signal by means of an electromagnetic wave or sonic wave into the medium and receiving the signal reflected from the object within the medium in the course of movement over the surface of the medium and a three-dimensional voxel data generating step of generating three-dimensional voxel data in the form of coordinates (x, y, t) consisting of a position (x, y) on the medium surface and a reflection time (t) based on intensity of the reflected signal; the method comprising: a maximum-magnitude extracting step of extracting, from the three-dimensional voxel data generated by the three-dimensional data generating step, a maximum value of the magnitude of the amplitude value and a reflection time tMAX providing the maximum value in the direction of reflection time (t) axis for each position (x, y) on the medium surface; a plane-locating step of locating, on an x-y plane of a predetermined reflection time (t), said maximum value and said reflection time tMAX extracted at said maximum-magnitude extracting step, respectively; an object-voxel selecting step at which said x-y plane having said maximum value located thereon is displayed and a coordinate point is designated on said displayed plane in accordance with a manual input operation, so that one or more object voxels are selected by specifying them with said designated coordinate point and said reflection time tMAX associated therewith; a binarizing step of extracting a candidate voxel group consisting of a plurality of voxels having amplitude values of positive or negative polarity and having magnitudes greater than a predetermined threshold and interconnected with each other; and a connecting/composing step of extracting, from the candidate voxel group extracted by the binarizing step, a connection-candidate voxel group to be connected to the object voxels selected by the object voxel selecting step and connecting said connection-candidate voxel group with said object voxels thereby to compose an object voxel group.
With the above-described characterizing feature, by executing the object voxel selecting step, the binarizing step and the connecting/composing step, from the candidate voxel group including a noise region comprised of unwanted reflected signals or the like having smaller reflected signal intensities, hence and having low likelihood of being the reflected signals from the object, the connection-candidate voxel group to be connected to the object voxels having high likelihood of being the reflected signals from the object is singled out and this group is connected and combined with the object voxels thereby to compose the object voxel group. With this, even when the threshold is set low, the large amount of noise region necessarily resulting therefrom can be effectively eliminated as being distinct from the object voxel group. Then, by simply setting the threshold higher, it is possible to prevent unwanted loss of the object voxel having higher likelihood of being a reflected signal from the object. Consequently, the exploration at a high S/N ratio is made possible.
Further, even in the case when a change in the exploring location leads to significant change in the reflected signal intensity, by first manually selecting the object voxel which represents a portion of the target object, the object voxel group connected continuously therefrom may be appropriately extracted, so that such continuously extending object as a buried pipe can be detected.
In addition, with this characterizing feature, when the object voxel(s) is (are) selected from the three-dimensional voxel data, the voxel to be designated is limited on the predetermined section. Thus, the object-voxel selecting step may be readily executed by means of a two-dimensional computer image display using a conventional CRT, a liquid crystal panel or the like and a manual computer input operation such as a cursor operation from a mouse or keyboard.
In addition, with the above characterizing feature, from the three-dimensional voxel data, the maximum value of the magnitude of the amplitude value and the associated reflection time tMAX are extracted and these maximum value and reflection time tMAX extracted for each position (x, y) on the medium surface are located respectively on the predetermined x-y plane inside or outside the three-dimensional voxel data, so that a section display may be provided for a maximum value of each position (x, y) on the medium surface. With this single section display (the x-y plane display), and, without effecting a plurality of section displays for various depths (reflection times (t)), the two-dimensional layout of a buried object at any depth can be grasped, thereby to allow easy and speedy selection of the object voxels, that is, extraction of the buried object.
Moreover, since such connecting/composing step can be carried out three-dimensionally, effective exploration result can be obtained also for a buried pipe or the like which is not oriented in the direction perpendicular to the scanning direction of the apparatus.
According to the second characterizing feature, the predetermined threshold utilized by the binarizing step is set based on the amplitude value of the object voxel selected by the object voxel selecting step.
Incidentally, the reflected signal intensity varies in accordance with the distance from the object to the surface of the medium or with the burying depth in the case of a buried object. Therefore, for exploring an area of shorter distance, it is necessary to set the threshold higher so as to eliminate the noise components effectively. Conversely, for exploring an area of longer distance, it is necessary to set the threshold lower to prevent loss of the object voxel.
Accordingly, with the second characterizing feature described above, the predetermined threshold utilized at the binarizing step is set based on the amplitude value of the object voxel selected by the object voxel selecting step. Hence, if the amplitude value of the object voxel is large, this is interpreted to indicate a short distance from the object to the medium surface, so that the threshold is set high correspondingly. The reverse setting thereof is also possible. As a result, with the selection of object voxel, the threshold can be set appropriately for the purpose of high S/N ratio extraction of the object corresponding to this object voxel. Moreover, this setting of threshold can be automated.
Moreover, in case the polarity of the candidate voxel group at the binarizing step is set in agreement with the polarity of the amplitude value of the object voxel, the threshold needs to be changed in accordance with this polarity. For instance, even when the zero value of the amplitude value is offset, the threshold can be appropriately adjusted based on the polarity of the amplitude value of the object voxel.
According to the third characterizing feature, in addition to the first characterizing feature described above, at the object voxel selecting step, said one or more object voxels are selected by substituting, for said designated coordinate point, a coordinate point which is present adjacent said designated coordinate point and which has the same polarity as the designated coordinate point and an amplitude value of the maximum magnitude.
With the above characterizing feature, when selecting the object voxel from the three-dimensional voxel data, if e.g., an operator errs in the computer input operation using a mouse or the like, thus failing to designate the correct object voxel and erroneously designating an adjacent voxel instead, it is still possible to select the correct object voxel having strong reflected signal intensity to be designated.
According to the fourth characterizing feature, the method effects a synthetic aperture operation or a migration operation on said three-dimensional voxel data or said candidate-voxel group or on said object voxel group.
With the above feature, by effecting the synthetic aperture operation or migration operation, it is possible to improve resolution within a plane (x, y) parallel to the medium surface.
In the above, if the synthetic aperture operation or migration operation is effected on the source three-dimensional voxel data consisting of raw data of the reflected signals, the three-dimensional voxel data comprise data which can approximate e.g. the buried condition of the object (i.e. information converted into the depth scale). So that, the analysis may proceed by setting the threshold with reference to the data, thus improving the convenience of use.
According to the fifth characterizing feature, at said three-dimensional voxel data generating step, a Wiener filtering operation or an amplitude adjusting operation is effected on the three-dimensional voxel data in the direction of the reflection time (t) axis, and the source three-dimensional voxel data before the processing is replaced by the processed data.
With the above characterizing feature, by effecting the Wiener filtering operation, the resolution in the direction of reflection time (t) axis may be improved. Also, by effecting the amplitude adjusting operation, amplitude of a weak reflected signal having a long reflection time can be enhanced.
For accomplishing the first object noted above, a three-dimensional exploring apparatus relating to the present invention has the sixth characterizing feature as follows.
According to the sixth characterizing feature, a three-dimensional exploring apparatus for finding location of an object present within a medium comprising; transmitting/receiving means for transmitting a wave signal by means of an electromagnetic wave or sonic wave into the medium and receiving the signal reflected from the object within the medium in the course of movement over the surface of the medium and three-dimensional voxel data generating means for generating three-dimensional voxel data in the form of coordinates (x, y, t) consisting of a position (x, y) on the medium surface and a reflection time (t) based on intensity of the reflected signal; wherein the apparatus further comprises: maximum-magnitude extracting means for extracting, from said three-dimensional voxel data generated by the three-dimensional voxel data generating means, a maximum magnitude value of the amplitude value and a reflection time tMAX providing the maximum value in the direction of the reflection time (t) axis for each position (x, y) on the medium surface; plane-locating means for locating, respectively on an x-y plane of a predetermined reflection time (t), said maximum value and said reflection time tMAX extracted by the maximum-magnitude extracting means; an object-voxel selecting means for displaying said x-y plane having said maximum value located thereon is displayed and designating a coordinate point on said displayed plane in accordance with a manual input operation, so that one or more object voxels are selected by specifying them with said designated coordinate point and said reflection time tMAX associated therewith; binarizing means for extracting a candidate voxel group consisting of a plurality of voxels having amplitude values of positive or negative polarity and magnitudes greater than a predetermined threshold and interconnected with each other; and connecting/composing means for extracting, from the candidate voxel group extracted by the binarizing means, a connection-candidate voxel group to be connected to the object voxels selected by the object voxel selecting means and combining said connection-candidate voxel group with said object voxels thereby to compose an object voxel group.
With the above-described characterizing feature, for the three-dimensional voxel data generated by the three-dimensional voxel data generating means, from the candidate voxel group including a noise region comprised of unwanted reflected signals or the like having smaller reflected signal intensities, hence and having low likelihood of being the reflected signals from the object, the connecting/composing means extracts only the connection-candidate voxel group to be connected to the object voxels selected by the object voxel selecting means and having high likelihood of being the reflected signals from the object and then connects and combines this group with the object voxels to compose the object voxel group. With this feature, even when the threshold is set low, the large amount of noise region necessarily resulting therefrom can be effectively eliminated as being distinct from the object voxel group. Thus, by simply setting the threshold higher, it is possible to prevent unwanted loss of the object voxel having higher likelihood of being a reflected signal from the object, so that the exploration at a high SIN ratio is made possible.
Moreover, with this characterizing feature, the three-dimensional exploring method having the above-described first characterizing feature of the invention can be employed. Therefore, the function/effect of the first characterizing feature can be achieved.
In addition, with this characterizing feature, by the section displaying means, it is possible to manually select and display a desired section of the three-dimensional voxel data generated by the three-dimensional voxel data generating means. Further, by the section coordinate-point designating means, it is possible to manually designate a coordinate point on the displayed section in accordance with a predetermined manual operation. Thus, when the object voxel(s) is (are) selected from the three-dimensional voxel data, it is possible to limit the voxel to be designated on the predetermined section. Therefore, the object-voxel selecting step may be readily executed by means of a two-dimensional computer image display using a conventional CRT, a liquid crystal display panel or the like and a manual computer input operation such as a cursor operation from a mouse or keyboard with reference to the display.
Further, as the x-y plane having the maximum value located thereon relating to the first characterizing feature is disposed inside or outside the three-dimensional voxel data, this plane is either included within the three-dimensional voxel data as a portion thereof, or serves to substantively extend the area of the three-dimensional voxel data in the direction of the reflection time (t) axis. Accordingly, this x-y plane having the maximum value located thereon is displayed as one section of the three-dimensional voxel data by the section displaying means.
A three-dimensional exploring method for accomplishing the second object relating to the present invention has the seventh or eighth characterizing feature as follows.
According to the seventh characterizing feature, in a three-dimensional exploring method for finding location of an object present within a medium by sequentially effecting an transmitting/receiving step of transmitting a wave signal by means of an electromagnetic wave or sonic wave into the medium and receiving the signal reflected from the object within the medium in the course of movement over the surface of the medium and a three-dimensional voxel data generating step of generating three-dimensional voxel data in the form of coordinates (x, y, t) consisting of a position (x, y) on the medium surface and a reflection time (t) based on intensity of the reflected signal, when the three-dimensional voxel data generated by the three-dimensional voxel data generating step contains a voxel deficient in data, the method effects, on said deficient voxel, a one-dimensional linear interpolation step of effecting a one-dimensional linear interpolation in a predetermined direction in an x-y plane including said deficient voxel when a distance along which the deficient voxels are present consecutively is shorter than a wavelength of the wave signal within said medium.
With this characterizing feature, the one-dimensional linear interpolation linearly interpolates between two source voxels for interpolating the deficient voxel therebetween. Therefore, even when another source voxel is present in the same direction as one nearer source voxel from the deficient voxel, the effect of the interpolation can be entirely free from influence from the data value of the distant source voxel. By the same operational principle, an extrapolation which is far less reliable will not be effected inadvertently. Further, supposing xe2x80x98nxe2x80x99 units of source voxels are present within the x-y plane i.e. a two-dimensional plane, then, the amount of calculation needed will be only on the order of (n). As a result, the processing time can be significantly reduced.
Consequently, a deficient voxel can be interpolated at high speed while the reliability of the interpolated value is maintained to an appropriate degree. Thus, in a situation where it is difficult to generate a complete set of three-dimensional voxel data due to certain restrictions present on the medium surface, highly efficient and highly precise exploration of a buried object is still possible.
In addition, with this characterizing feature, it is possible to appropriately restrict execution of the interpolating operation between two source voxels which are too far apart from each other to ensure linear interpolation with high precision. As a result, it becomes possible to avoid forcible execution of interpolation with poor precision. And, a deficient voxel present between such source voxels can be recognized as such for indicating it as un-measurable region dearly and this indication can help improve the exploration precision at the measurable region. Further, if this feature is combined with the eighth feature described above, since there can be a case where the one-dimensional linear interpolation is impossible in one direction but possible in another direction, it becomes possible to avoid forcible execution of low-precision interpolation, thereby improving the exploration precision.
Incidentally, the reason why the wavelength of the wave signal within the medium is employed for the judgement whether to effect the one-dimensional linear interpolation or not is based mostly on the experiments.
According to the eighth characterizing feature, said linear interpolation step is effected for two or more times with varying the direction of the one-dimensional linear interpolation.
With this charactelizing,feature, even when the two-dimensional distribution of source voxels within the x-y plane is rather random, the interpolation can be done in a sufficiently dense manner to interpolate all of the deficient voxels in the end.
The characterizing feature of a three-dimensional exploring apparatus for accomplishing the second object is the ninth characterizing feature as follows.
According to the ninth characterizing feature, a three-dimensional exploring apparatus for finding location of an object present within a medium, including transmitting/receiving means for transmitting a wave signal by means of an electromagnetic wave or sonic wave into the medium and receiving the signal reflected from the object within the medium in the course of movement over the surface of the medium and three-dimensional voxel data generating means for generating three-dimensional voxel data in the form of coordinates (x, y, t) consisting of a position (x, y) on the medium surface and a reflection time (t) based on intensity of the reflected signal, the apparatus comprises linear interpolating means for effecting, when the three-dimensional voxel data generated by the three-dimensional voxel data generating step contains a voxel deficient in data, on said deficient voxel, a one-dimensional linear interpolation in a predetermined direction in an x-y plane including said deficient voxel when a distance along which the deficient voxels are present consecutively is shorter than a wavelength of the wave signal within said medium.
With this characterizing feature, the linear interpolating means effects a one-dimensional linear interpolation in a predetermined direction on the x-y plane, thus executing the linear interpolation step of the above-described tenth characterizing feature. Alternately, the linear interpolating means effects a one-dimensional linear interpolation in a first direction on the x-y plane and effects again another one-dimensional linear interpolation with changing the direction of effecting the linear interpolation, so that with repeated execution of linear interpolating operations in the same manner as needed, the linear interpolation step of the above-described eighth characterizing feature is effected. In these manners, the same functions/effects of the seventh or seventh and eighth characterizing features can be achieved.
For accomplishing the third object described above, a three-dimensional voxel data displaying method relating to the present invention has the tenth through sixteenth characterizing features as follows.
According to the tenth characterizing feature, in a method of displaying three-dimensional voxel data generated in the form of coordinates (x, y, t) consisting of a position (x, y) on a medium surface and a reflection time (t) based on intensity of a reflected signal of a wave signal transmitted from a surface of a medium into the medium and reflected therefrom, the method executes: for said three-dimensional voxel data, a maximum-magnitude extracting step of extracting a maximum magnitude value of the amplitude value in the direction of the reflection time (t) axis for each position (x, y) on the medium surface, a plane-locating step of locating said maximum magnitude value on a predetermined plane for each position (x, y) on the medium surface extracted by said maximum-value extracting step, and a plane displaying step of displaying said maximum magnitude value located on said predetermined plane.
With the above characterizing feature, for the three-dimensional voxel data, a maximum magnitude value of the amplitude value in the direction of reflection time (t) axis is extracted for each position (x, y) on the medium surface and this maximum magnitude value for each position (x, y) on each medium surface is located and displayed on a predetermined plane. Accordingly, even when the S/N ratio of the three-dimensional voxel data is low and the area of the object within the medium is relatively small compared with the entire area to be explored, high-contrast display may be provided as long as areas of strong reflected signals exist in a localized manner. So that, the two-dimensional layout of the object can be readily grasped with high visibility.
According to the eleventh characterizing feature, a maximum value and a minimum value are obtained from the maximum magnitude values extracted at said maximum magnitude extracting step and the maximum magnitude values are normalized such that said maximum value and said minimum value respectively become an upper limit and a lower limit of display scale.
With this characterizing feature, in locating and displaying the maximum magnitude values for each position (x, y) on each medium surface on the predetermined plane, the maximum value and the minimum value are obtained from those maximum magnitude values. Then, the maximum magnitude values are normalized such that said maximum value and said minimum value respectively become an upper limit and a lower limit of display scale. Therefore, the contrast may be further enhanced for additional improvement of the visibility.
According to the twelfth characterizing feature, at said maximum magnitude extracting step for extracting the maximum magnitude values for each position (x, y) on the medium surface, a reflection time tMAX providing the maximum magnitude values is also extracted.
With this characterizing feature, at the maximum magnitude extracting step for extracting the maximum magnitude values of the amplitude value in the direction of reflection time (t) axis for each position (x, y) on the medium surface, the reflection time they providing the maximum magnitude values is also extracted. Hence, it becomes readily possible to grasp at which reflection time (t) (corresponding to the distance from the medium surface, or to the burying depth in the case of underground buried object exploration) the object area transmitting strong signals is present.
According to the thirteenth characterizing feature, at the maximum magnitude extracting step for extracting the maximum magnitude values of the amplitude value in the direction of reflection time (t) axis for each position (x, y) on the medium surface, any amplitude values outside a predetermined range of reflection time (t) are excluded.
With this characterizing feature, in extracting the maximum magnitude values of the amplitude values in the direction of reflection time (t) axis for each position (x, y) on the medium surface, any amplitude values outside a predetermined range of reflection time (t) are excluded. Therefore, it becomes possible to exclude any area, such as an area near the ground surface or underground water surface in the case of an underground exploration, where the reflected signal intensity within the medium becomes extremely high. As a result, it becomes possible to improve the visibility for the area of the object inside the medium (the buried object area in the case of underground exploration).
According to the fourteenth characterizing feature, at the maximum magnitude extracting step for extracting the maximum magnitude values of the amplitude values in the direction of reflection time (t) axis for each position (x, y) on the medium surface, only either voxels whose amplitude value polarity is positive or negative are used for the extracting step.
With this characterizing feature, in extracting the maximum magnitude values of the amplitude values in the direction of reflection time (t) axis for each position (x, y) on the medium surface, only either voxels whose amplitude value polarity is positive or negative are used for this extracting step. So that, the extracting step is effected for only those amplitude values having a polarity of higher S/N ratio of the reflected signals from the object in the medium., Consequently, the visibility of the area of the object in the medium can be improved. This feature is provided in consideration of the fact that in the case of underground buried object exploration, the polarity of the reflection coefficient of the transmitted signal from the buried object varies depending on the kind of material forming the buried object. For instance, the reflection coefficient is negative for a metal pipe and the coefficient is positive for a resin pipe or hollow cave.
According to the fifteenth characterizing feature, prior to the maximum magnitude extracting step, a synthetic aperture operation or a migration operation is effected on three-dimensional voxel data consisting of the reflected signal intensity so as to generate said three-dimensional voxel data to be displayed.
With this characterizing feature, by effecting the synthetic aperture operation or migration operation, the resolution within an x-y plane parallel to the medium surface may be improved. Further, since the three-dimensional voxel data obtained by effecting the synthetic aperture operation or migration operation on the source three-dimensional voxel data consisting of raw data of the reflected signals can become data which approximate e.g. the buried condition of the object (i.e. information converted into the depth scale). Therefore, the visibility can be further improved.
According to the sixteenth characterizing feature, said synthetic aperture operation or migration operation is effected at various propagation velocities in various kinds of medium to obtain a set of the three-dimensional voxel data for each propagation, said maximum magnitude extracting step and said plane locating step are effected for each set of three-dimensional voxel data associated with each propagation velocity, and a processing result at an appropriate propagation velocity is selected based on the displayed results of the sets of the three-dimensional voxel data at said plane displaying step for each propagation velocity.
With this characterizing feature, the synthetic aperture operation or migration operation is effected using various propagation velocities of various kinds of medium and each set of three-dimensional voxel data generated for each propagation velocity is displayed at the plane displaying step for evaluation of focus condition of the displayed result. With these, even when the propagation velocity in the medium is unknown, it is still readily possible to select the processing result at an appropriate propagation velocity. As a result, high resolution within the x-y plane parallel to the medium surface may be assured.
For accomplishing the third object noted above, a three-dimensional voxel data displaying apparatus relating to the present invention has the seventeenth characterizing feature as follows.
According to the seventeenth characterizing feature, an apparatus for displaying three-dimensional voxel data generated in the form of coordinates (x, y, t) consisting of a position (x, y) on a medium surface and a reflection time (t) based on intensity of a reflected signal of a wave signal transmitted from the surface medium into the medium and reflected therefrom, the apparatus comprises: maximum-magnitude extracting means for extracting from said three-dimensional voxel data, a maximum magnitude value of the amplitude value in the direction of the reflection time (t) axis for each position (x, y) on the medium surface; plane-locating means for locating said maximum magnitude value on a predetermined plane for each position (x, y) on the medium surface extracted by said maximum-value extracting means; and plane displaying means for displaying said maximum magnitude value located on said predetermined plane.
This three-dimensional voxel data displaying apparatus can be employed for carrying out the three-dimensional voxel data displaying method having the above-described tenth through sixteenth and its basic functions/effects are identical to the functions/effects of the three-dimensional voxel data displaying method having the above-described tenth characterizing feature.